The present invention generally relates to sensing devices and sensing techniques thereof. The present invention also relates to magnetic sensors. Additionally, the present invention relates to rotary position sensors. The present invention is also related to cam and crank applications, such as camshaft and crankshaft devices.
A variety of techniques are utilized for angular position sensing. Optical, resistive, electrical, and electrostatic and magnetic fields have all been utilized with sensing devices to measure position. There are many known devices that utilize optical, resistive, electrical, magnetic and other such energies for sensing. Examples of such sensing devices include resistive contacting sensors, inductively coupled ratio detectors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors utilizing the Faraday effect, photo-activated ratio detectors, radio wave directional comparators, and electrostatic ratio detectors. In addition, there are many other sensors/detectors that are not mentioned herein.
Each of these detection methods offers much value for one or more applications, but none meet all application requirements for all position sensing applications. The limitations may be due to cost, sensitivity to particular energies and fields, resistance to contamination and environment, stability, ruggedness, linearity, precision, or other similar factors. Transportation applications generally, and specifically automotive applications, are very demanding.
In mechanical and/or electromechanical systems, such as for example, automotive applications, motion can be initiated and controlled by rotating a member such as a shaft (e.g., camshaft, crankshaft, and so forth). The angular motion of the shaft is then translated into some other motion, such as linear displacement, rotation of a pump or fan, or the angular rotation of some other intermediate part at a different angular velocity or spatial orientation. Numerous mechanical means such as gears, cams, pulleys, and belts are commonly employed in translating the angular motion of an input shaft to drive an output device. Camshaft and crankshaft mechanisms, for example, are well known in the mechanical transportation arts. Thus, a need exists for sensors that can properly monitor motion and position in such mechanical systems.
In engine cam and crank applications, for example, recently manufactured cars require precision rotary sensors for high performance and fuel economy. In particular, some of the new camless engines require precision rotary sensors. Such engines utilize electrical-mechanical solenoids to control the engine valves. The opening and closing of such valves are not controlled by a fixed cam but can be controlled by a microprocessor that receive inputs from precision rotary sensors regarding the crank, speed, torque, load, exhaust gas mixture, oxygen content, and so forth. In this manner, an engine can be achieved that is both efficient and high performing.
Thus, a critical need exists for high performance camshaft and crankshaft position sensors. Major automakers worldwide are presently working, for example, on camless four-stroke engines because of potential performance advantages and reduction in mechanical components subject to wear. A number of development hurdles must be overcome before such mechanical systems can be widely deployed. Cost will limit the camless engine to high-performance cars for some time. Obviously, camless engines do not require a camshaft sensor. On the other hand, valve position sensors will very likely be needed. Developers are presently faced with the challenge of creating cost-effective solutions now, in anticipation of this emerging need. As transport systems develop in their complexity and performance, a need has emerged for non-contact rotary position sensors, which offer significant durability enhancements, lower cost, and improved performance.
Rotary position sensors play a particularly critical role in crankshaft applications used in automotive and other transport systems (e.g., trucking, aerospace, etc.), because the U.S. government requires misfire detection as part of the On-Board Diagnostics incorporated in the engine control system to detect failures of any components of the system. Such failures could result in emissions not being controlled within the proper limits. The misfire event must be identified down to a specific cylinder except at low loads and high rpm. A xe2x80x9cmisfirexe2x80x9d is generally known as an absence of combustion in one or more cylinders, either occurring singly or multiple times. It can be caused by a failure of the ignition system to provide spark or by a failure in the fuel injection system resulting in fuel not being provided to a cylinder. It differs from xe2x80x9cknockxe2x80x9d, which is spontaneous ignition of the fuel-air mixture. Knock can result in engine damage and is a function of several parameters of both the engine and the fuel used. Engines expected to operate on a variety of fuels usually incorporate a knock detection and prevention function in the engine control system. Misfires typically do not result in engine damage but may cause failure of the catalytic converter if it has to cope with unburned gases.
Each time ignition occurs, the resulting power stroke accelerates the crankshaft and it then decelerates at a rate determined by the load on the engine. The basic equation governing crankshaft angular acceleration/deceleration is as follows: xcex1=dxcfx89/dt=d2xcex8/dt2=(TPxe2x88x92TL)/I, where TP=Torque produced by engine, TL=Load torque, and I=Moment of inertia of drive train.
A four-stroke engine, for example, produces N/2 torque pulses per crankshaft revolution, where N=number of cylinders. For a constant load torque, the crankshaft accelerates each time a combustion event occurs, followed by a deceleration due to the load torque. By measuring these speed fluctuations, misfires can be detected since a larger deceleration will occur if one or more firing pulses are missed. For a fixed engine displacement, each power pulse becomes smaller as the number of cylinders increases, reducing the magnitude of the speed fluctuations. Likewise, as the load on the engine decreases, the engine decelerates less between power pulses. A variation in load torque due to a bump in the road may also result in a crankshaft speed fluctuation and possibly be confused with a misfire. The misfire detection algorithm is disabled when load torque fluctuations occur, either by an accelerometer signal or by monitoring wheel speed fluctuations. The crankshaft speed fluctuation method is the most widely used approach since most engines already incorporate a crankshaft position sensor.
To be usable for misfire detection by the crankshaft speed fluctuation method, a sensor must have excellent repeatability. Repeatability is affected primarily by the sensor""s sensitivity to dynamic radial and axial run-out of the target and by the signal-to-noise ratio of the sensor. Generally, a target can be made wide enough so that axial run-out does not result in any error. The error due to dynamic radial run-out is proportional to the error as a function of air gap so that a sensor with minimum error as a function of air gap is preferred. Typical gear tooth sensors have three main error sources: air gap error, speed error, and temperature error. In general, auto manufacturers desire precision rotary sensors for gearshift levers (e.g., P, R, N, 1, 2, 3, DR). In addition, new automobiles require an absolute rotary position at startup and cannot wait for one or more revolutions of the crank to find the top dead center (TDC) as with gear tooth rotary sensors.
Thus, it can be appreciated that it is very desirable to monitor the position of various mechanical parts within a mechanical system. In many cases, however, due to space restrictions or other physical characteristics, it is inconvenient or impossible to directly monitor the position of a particular part. In such cases it is often easier to monitor the position of the part indirectly. For example, in the mechanisms described above, measuring the angular position of the front wheels directly would be a difficult and expensive proposition. Thus, by utilizing a rotary position sensor in association with an automobile, it is possible to generate an electrical signal, which indicates the angular position of the front wheels.
The relationship between the angular position of a rotating input shaft and the position of an output or intermediate mechanical member is ubiquitous throughout the mechanical arts. In some applications, such as servomotors, a position sensor is mounted directly to the output shaft of a motor, and the output position and/or speed of the machine can be readily determined by monitoring the rotation of the motor. In any mechanical system wherein the output position of a mechanical part is to be determined by the position of a rotating input shaft, a key element is the rotary position sensor.
A rotary position sensor must accurately and reliably determine the angular position of the input shaft before that information can be extrapolated into the position of the output member. In addition to accuracy and reliability issues, each specific application will provide its own demands and limitations on the design of the rotary position sensor.
In some systems it may only be necessary to sense rotation over a single turn. In still other applications, physical constraints may make it difficult to couple electrical signals to the rotating portion of the sensor. And finally, the cost of various position sensors may be an overriding factor in determining the best sensor for a particular application.
Some rotary position sensors currently in use include rotary potentiometers, inductive position resolvers, and optical encoders. Each device has characteristic advantages and disadvantages, which make some devices more suitable for particular applications than for others. Rotary potentiometers, for example, supply a voltage signal proportional to the position of a wiper contact, which rides along a resistive element. Initially, such rotary potentiometers are quite accurate and provide excellent position indication over a single turn of the input shaft. Over time, however, the sliding motion of the wiper contact over the resistive element can lead to wear which alters the resistance ratio between the resistive element and the wiper contact, leading to inaccuracy in the output position signal.
Rotary potentiometers are also subject to contamination of the contact elements, which can adversely affect the accuracy of the device. For these reasons, rotary potentiometers are not well suited for those applications where extended long-term reliability is required or where harsh environmental conditions are likely to adversely affect the sensor. Thus, a rotary potentiometer would be particularly unsuited for application in the crankshaft and camshaft mechanisms described above.
Inductive position resolvers, on the other hand, have advantages over rotary potentiometers in that they are non-contact devices. Resolvers operate on inductive principles, having mutually coupled coils mounted to both a rotor and a stator. As the rotor coil rotates relative to the stator coil, the mutual inductance between the two coils changes such that a voltage signal impressed on the stator coil will be coupled to the rotor coil in varying strength depending on the angular relationship between the coils. While resolvers have obvious advantages over rotary potentiometers, a drawback is that they require signal connections to the rotating member. Therefore, slip rings or some other mechanism for connecting electrical signals to the rotating member are required. Also, resolvers are generally more expensive than rotary potentiometers and more sensitive to vibration and shock.
Finally, optical encoders are often used as rotary position sensors, but such devices also offer significant drawbacks for certain applications. As with resolvers, optical encoders tend to be expensive, thus making them inappropriate for those applications where low cost is a critical design factor. Furthermore, encoders are digital devices, emitting light pulses for each fraction of a rotation of the input shaft. The resolution of an encoder is determined by physical limitations in the number of pulses, which can be generated per revolution of the input shaft. Thus, optical encoders are inappropriate for applications where a continuous analog signal is required. In particular, such devices are not well suited for camshaft and crankshaft mechanisms.
It can thus be appreciated based on the foregoing that in many automotive and transportation applications, a low-cost, durable analog sensor is required. In most such cases a non-contact type sensor is preferred where the rotating member within the sensor has no physical contact with the stator in order to prevent wear between the rotating parts. In some cases it may be necessary to provide a non-contact rotary sensor where there are no electrical connections required for coupling signal to the rotating member. In still other cases it may be necessary to provide a rotary position sensor where the sensor provides a continuous analog signal over a multi-turn range of the input shaft.
The automotive and other transportation industries (e.g., aerospace, trucking, heavy equipment, etc.) thus require absolute precision rotary sensors for increased demands for a cleaner environment, increased fuel economy, and better performance. Rotary sensors generally must be configured as non-contact rotary sensors for accuracy of less than one degree and should operate continuously through 360 degrees.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide an improved sensing device and sensing technique thereof.
It is still another aspect of the present invention to provide an improved magnetic-based sensor.
It is yet another aspect of the present invention to provide an improved rotary position sensor.
It is also an aspect of the present invention to provide an improved rotary position sensor that can be utilized in association with engine cam and crank applications.
The above and other aspects can be achieved as is now described. An apparatus and method are disclosed herein for sensing rotary position in automotive, transportation and other mechanical and electro-mechanical applications. Generally, a rotor and stator are positioned proximate to one another but are not in contact with one another. The rotor comprises at least one radial spoke for receiving angular information from the stator, wherein the rotor is located in a non-contact position proximate to the stator. Preferably, the rotor comprises only one radial spoke for receiving the angular information from the stator. Additionally, a coil or other transmitting member can be located centrally between the stator and the rotor, wherein the angular information is broadcast to the stator from the rotor through the coil to resolve angles between spoke positions thereof and thereby accurately sense a rotary position.
The rotor comprises a passive rotor and includes a transmitting coil associated with the rotor. A receiving coil is associated with the stator. Additionally, at least one transmitting spoke is associated with the stator. Such a transmitting spoke transmits a delayed signal in electrical degrees comprising data indicative of a physical location of one or more transmitting spokes on the stator. The stator also can be associated with a digital phase generator ASIC (application specific integrated circuit). The stator is thus generally configured to include a stator transmitter and a stator receiver.
The present invention generally comprises two discs (i.e., a stator and a rotor) that can be fabricated utilizing standard PC board technologies. The rotor (i.e., rotor disc) is not in contact with the stator (i.e., stator disc). The rotor is completely passive (i.e., no active components) and comprises a single radial spoke for receiving angular information from the stator and re-broadcasting this information back to the stator by means of coils located near the center of the rotor and the stator. The stator has N transmitting spokes, wherein each spoke can transmit a delayed signal in electrical degrees that corresponds exactly to the physical location of the spoke on the stator disc.